The present invention relates to a method for determining core positions of an optical element array and an apparatus for determining core positions thereof. More particularly, the present invention relates to a method for determining core positions of an optical element array and an apparatus for determining core positions thereof capable of conveniently determining core positions of optical elements (optical fibers, lenses, and the like) on a substrate with high accuracy.
In recent years, accompanied by an increase in the capacity of data communications, there has been an increased demand for optical cross-connect switch technology excelling in processing capability for a large capacity of data communications. As one type of such technology, an optical switch manufactured using a MEMS (micro-electro-mechanical system), which is a technology used for micromachining in which fine processing is performed by a semiconductor process such as silicon etching, has been used. A surface-emiffing laser, which enables high-definition and stable communications, has also been used, accompanied by an increased demand for securing reliability in addition to the demand for processing capability.
An optical element array, (examples of which include an optical fiber array, a lens array, a waveguide array (planar lightwave circuit: PLC), a semiconductor laser (LD) array, and a photodiode (PD) array) is used for the optical switch and the surface-emiffing laser. It is necessary to determine the core positions of the optical fiber array with high accuracy from the viewpoint of decreasing light loss due to the connection and stability of the connection section. To deal with this demand, various methods for determining core positions of an optical element array, and apparatus for determining core positions thereof utilizing these methods have been used.
For example, in a method for determining core positions of an optical fiber array using a conventional apparatus for determining core positions of an optical fiber array, white light or the like applied from a light source installed on the back of a stage is caused to be incident on one end face of the optical fiber of the optical fiber array installed on the stage, and the light, which is allowed to pass through the core and is emitted from the other end face of the optical fiber, is imaged by using imaging means such as a CCD camera. The core position of the optical fiber array is determined by analyzing the resulting image using a specific analysist method.
However, in the conventional method for determining core positions, when the end face of the optical fiber array facing the imaging means is not horizontal to the imaging direction, the light emitted from the end face of the optical fiber array may be refracted due to the shape (angle-cut shape) of the end face, and the optical axis may deviate from the optical axis of the CCD camera, or the optical fiber array may be installed in the stage in a state in which the optical axis of the end face of the optical fiber array deviates from the optical axis of the CCD camera. This gives rise to problems in which the center position of the core displayed in the image varies depending on the imaging position (focus) of the imaging means such as the CCD camera from the end face of an optical fiber array 60, as shown in FIGS. 10(a) and (b).
If the imaging position (focus) of the imaging means such as the CCD camera varies between each determination of the core position, a determination error may occur when repeatedly determining the same core. Generally, the relative positional relation between each core is important for accuracy of the core positions of the optical fiber array. If the distance between the imaging position and the end face of the optical fiber array is equal, since each core to be imaged is merely shifted to either left or right at an equal distance, a change in the relative positional relation between the core positions does not occur, even if the optical axis of the light emitted from the end face of the optical fiber array deviates from the optical axis of the CCD camera. Therefore, the above problem occurs in the case where the imaging position (focus) of the imaging means varies between imaging of each core, and each core in the resulting image is shifted to the right or left, whereby the relative positional relation between each core differs each time the core position is determined. If the core position is determined under such conditions, the core position cannot be determined with high accuracy.
In the conventional method for determining core positions, when image processing the core of the optical fiber array by using the CCD camera or the like, the position of the core displayed on the display screen may vary during the determination of the core position of a multi-core array due to the pitch accuracy of the optical fiber array, the moving accuracy of the stage, and the like, even if imaging is started in a state in which the core is displayed at the center of the display screen which displays the image taken by the imaging means.
If the position of the core displayed on the display screen differs between each imaging, the core is imaged using different areas of the lens such as that of the CCD camera which images the core. This results in problems in which an image taken using the center of the lens may differ from an image taken using the edge of the lens due to aberration of the lens, or the shapes of the imaged cores may vary since the pixel distribution of the CCD camera or the like is changed each time the core is imaged, whereby the position of the core cannot be determined with accuracy.
In the conventional method for determining core positions, in the case where the optical fiber array is installed in a stage 64 in a tilted state as shown in FIG. 11, a distance A (hereinafter may be called “determination x”) projected on a horizontal plane (xz plane) between two points of the adjacent optical fibers of the optical fiber array 60 which intersect a plane perpendicular to the imaging direction (z direction) is determined in the determination by image processing using the CCD camera or the like. However, the determination x differs from a distance B (hereinafter may be called “true value x”) projected on the horizontal plane (xz plane) between two points of the optical fibers 62 which intersect a plane perpendicular to the central axes of the optical fibers in the horizontal plane (xz plane), which is originally required for the determination of the core positions of the optical fiber array 60. Therefore, the loss of light due to the connection may occur or the connection section may become unstable if the core positions are calculated using the determination x.
In particular, in the case where the optical fiber array 60 is manufactured by obliquely cuffing the end face in advance, if the optical fiber array 60 is installed on the stage 64 of the apparatus for determining core positions so that the axis of the light emitted from the end face is parallel to the imaging axis, an angle C (hereinafter may be called “array θx”) formed by the plane perpendicular to the center axes of the optical fibers 62 and the side of the optical fiber array 60 from which the light is emitted is increased on the horizontal plane (xz plane). If the core position is imaged in this state, since the difference D (hereinafter may be called “determination z”) in the distance between the imaging means 61 and the end faces of each optical fiber 62 from which the light is emitted is increased in the imaging direction (z direction), the distance at which the stage is driven in the z direction during imaging is inevitably increased. Since an error in the distance accompanied by driving the stage is increased as the drive distance is increased, a large error may occur when calculating the core position by correcting the array θx.
In the conventional method for determining core positions, a distance (hereinafter may be called “determination y”) projected on a vertical plane (yz plane) between two points of the adjacent optical fibers of the optical fiber array which intersect a plane perpendicular to the imaging direction (z direction) differs from a distance (hereinafter may be called “true value y”) projected on the vertical plane (yz plane) between two points of the adjacent optical fibers which intersect the plane perpendicular to the center axes of the optical fibers, which is originally required for the determination of the core positions of the optical fiber array. Therefore, the loss of light due to the connection may occur or the connection section may become unstable if the core positions are calculated by using the determination y. The core position is imaged by disposing an angle spacer having a specific correction tilt angle (hereinafter may be called “jig θy”) on the stage depending on a tilt angle (hereinafter may be called “array θy”) on the vertical plane (yz plane) formed by the plane perpendicular to the center axes of the optical fibers and the side of the optical fiber array from which the light is emitted. However, since the resulting determined value may differ from the true value y, this is insufficient for the determination of the core positions for which high accuracy is necessary.